Chiller structure for refrigeration systems



Dem 1969 R. A. ENGLISH CHILLER STRUCTURE FOR REFRIGERATION SYSTEMS Filed June 7, 1968 INVENTOR.

RICHARD A. ENGLISH. BY

15 F UM.

ATTORNEY.

8. v o \NN o o O x 0 Y7 O v8 0 United States Patent 0,

US. C]. 62-85 5 Claims ABSTRACT OF THE DISCLOSURE A refrigeration system comprised of a generator, solution-cooled absorber, primary absorber, condenser, liquidsuction heat absorber, and chiller, the heat exchanger interiorly of the chiller being constructed of a non-hardening ferritic stainless steel of relatively low chromium content having superior corrosion resistance.

BACKGROUND OF THE INVENTION The present invention relates to a gas air conditioning system having a chiller as one portion thereof and featuring therein a coil construction for passage of refrigerant therethrough composed of an alloy of relatively low cost, excellent oxidation and corrosion resistance and also posesses ease of weldability. The material utilized for this purpose is a non-hardening ferritic stainless steel having a relatively low chromium content and also including therein compounds having stabilizing and passivating influences.

Coil constructions for chillers or evaporators conventionally are of galvanized mild steel tubing welded in sections. Apparently, as a result of the welded joints, there develops ammonia seepage, causing attacks on the zinc coating and producing perforations in the tubing. Also, in the prior art constructions, inhibitors or other water treatment materials are required to reduce the detrimental effects of such ions as chloride or bicarbonate which induce corrosion and ultimately produce crevices in the coils.

SUMMARY OF THE INVENTION The instant invention is particularly directed to a chiller package for use as an integral part of a refrigeration system, the chiller package embodying therein a tubular member for passage of refrigerant therethrough. The novel aspect of this invention is the construction of the tubular heat exchanger from a non-hardening ferritic stainless steel which during its formulation includes carbon, manganese, silicon, nickel, iron, chromium as a passivator and titanium as a carbide stabilizer. The alloy has a relatively low chromium content and it has been found that a coil arrangement so constructed is remarkably resistant to corrosion and oxidation, is of relatively low cost, possesses ease of weldability, and essentially avoids the need for inhibitors or other water treatment materials.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 illustrates schematically, and with portions thereof taken in section, a preferred form of air conditioning system; and

FIGURE 2 is a fragmentary sectional view of an addi tional form of the invention wherein both the chiller casing and coil member are of stainless steel.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, there is shown a refrigeration system comprising a primary absorber 10, a condenser 11, an evaporator or chiller 12 which forms the Patented Dec. 2, 1969 ice subject matter of the present invention, a generator 13, a solution-cooled absorber 14 and a liquid-suction heat exchanger 15 connected to provide a refrigeration cycle. A pump 16 is employed to circulate weak absorbent solution from the primary absorber 10 to the generator 13. As used herein, the term weak absorbent solution refers to a solution which is weak in absorbent power and the expression strong absorbent solution refers to a solution which is strong in absorbent power. A suitable absorbent solution for use in the system described is water and a suitable refrigerant is ammonia.

Liquid refrigerant condensed in the condenser 11 passes through refrigerant liquid passage 18, and refrigerant restriction 20 to heat exchange tube 22 of the liquid-suction heat exchanger 15. The liquid refrigerant is cooled in the tube 22 and emerges from the liquid-suction heat exchanger and passes through refrigerant restriction 24 into heat exchanger 26 in the chiller 12.

A fluid medium such as water to be chilled passes over the exterior of the heat exchanger 26, where it is chilled by giving up heat to evaporate refrigerant within the heat exchanger. The chilled medium passes out of the chiller 12 through line 28 to suitable remotely located heat exchangers (not shown), after which it is returned to the chiller through inlet 30 for rechilling.

The cold refrigerant evaporated in the heat exchanger 26 passes through refrigerant vapor passage 32 and through the liquid-suction heat exchanger 15 in heat exchange relation with liquid refrigerant passing through the tube 22. The refrigerant vapor then passes through refrigerant vapor passage 34 into the solution cooled absorber 14.

The solution cooled absorber 14 is formed within a tubular or cylindrical vessel 38 by a tubular, preferably cylindrical, internal baffle 36 which divides the tubular cylindrical vessel 38 into the solution cooled absorber 14 and a second solution chamber 40. The vessel 38 is preferably closed at opposite ends. The baflle 36 may be provided with a top cover plate 39 having a plurality of vapor discharge apertures 42 therein to allow vapor to escape from the solution cooled absorber 14 into the chamber 40.

A weak solution heat exchanger 44 preferably comprising a helical coil is disposed within solution-cooled absorber 14. A plurality of horizontally extending plates 46 are secured to a central support 48 and arranged interiorly of the baffle 36 to cooperate with annular grooves 50 and the heat exchanger 44 to provide a tortuous continual flow or passage for vapor and solution through the solution cooled absorber 14. Suitable packing means, such as Raschig rings 52, may chill the space between the uppermost plate 46 and the top of solution cooled absorber to reduce the tendency for solution froth to escape through the discharge apertures 42.

A refrigerant vapor distributor header 54 is secured to close the bottom of the bafiie 36. The header 54 is provided with refrigerant vapor ports 56 for passage of refrigerant vapor from the line 34 into the solution cooled absorber 14 and the chamber 40. Strong solution from the generator 13 is admitted to the top portion of the solution cooled absorber 14 through line 58. The strong solution passes downwardly through the solution cooled absorber in counter-flow relation with upwardly passing refrigerant vapor and weak solution passing through the coil 44. A strong solution discharge passage 60 is provided adjacent the lower portion of the batfie 36 for passage of solution from the solution cooled absorber into the chamber 40.

Solution discharge passages 62 are provided for passing a mixture of refrigerant vapor and solution from the chamber 40 to the primary absorber 10. Each of the discharge passages comprises a tubular member having open upper ends for admission of vapor and a solution inlet aperture 64 disposed below the level of absorbent solution in the chamber 40. This insures a mixed flow of liquid and vapor to the primary absorber.

A cooling medium, preferably ambient air, is passed through the primary absorber in heat exchange relation with the absorbent solution to cool the absorbent solution and promote the absorption of the refrigerant vapor in the absorber. The same cooling medium may be supplied to the condenser 11 in heat exchange relation with refrigerant therein to condense the refrigerant.

Cold weak absorbent solution passes from the primary absorber 10 through line 66 into pump inlet tank 68. Weak solution from the inlet tank 68 is supplied to Weak solution pump 16 through line 72. Liquid from pump 16 passes through pump discharge tank 74 to a rectifier heat exchange coil 74 to a rectifier heat exchange coil 76- From the coil 76 the weak solution passes through line 78 to the Weak solution heat exchanger 44 in the solution cooled absorber 14. The weak solution from the coil 44 passes through line 80 into the upper portion of the generator 13 along any vapor formed in the coil 44.

The generator 13 comprises a shell 82 having fins 84 suitably aflixed thereto, as by welding. The generator is heated by a gas burner 86 or any other desired heating means. The weak solution is boiled in the generator 13 to form a strong solution and refrigerant vapor.

The hot strong absorbent solution passes upwardly through the analyzer section of the generator 13 through analyzer coil 88 in heat exchange relationship with the weak'solution passing downwardly over the coil. The warm strong solution then passes through the line 58 which has a solution restricter 87, and is then discharged into the upper portion of the solution cooled absorber 14.

Refrigerant vapor formed in the generator 13 passes upwardly through the analyzer section thereof where it is concentrated by mass transfer with weak solution passing downwardly over the analyzer coil 88. Analyzer plates 90 in the generator 13 provides a tortuous path for flow of solution and vapor to assure intimate contact therebetween to improve the mass transfer. The refrigerant vapor from the analyzer section passes through reflux plate 92 in heat exchange relation with absorbent condensed in rectifier 94. The vapor then passes through the rectifier 94 in heat exchange relation with the rectifier heat exchange coil 76. Absorbent condensed in the rectifier 94 flows downwardly onto the plate 92 where it is heated by the refrigerant vapor passing therethrough. The heated absorbent is then passed to the generator along with the weak solution discharged into the generator from line 80. Vapor passes through line 96 to the condenser 11 to complete the refrigeration cycle.

The water chiller 12 illustrated comprises an outer cylindrical shell 102 having a top member 104 secured thereto. A cylindrical liner 106 is disposed within the shell 102 in spaced relation thereto. A suitable insulating material 108 such as polyurethane or polystyrene foam is provided between the shell 102 and the liner 106 and along the bottom of the liner. The insulation is preferably foamed in place to form a complete assembly. The heat exchanger 26 in the chiller 12 is disposed intcriorly of the liner 106 for passage of refrigerant therethrough. A distribution tray 110 which is disposed above the heat exchanger 26 receives water returned from the remote heat exchangers through return water line 30. The distribution tray 110 is provided with two concentric rows of downwardly directed nozzles 112 which are aligned above the two rows of coil 26 for discharge of water from the tray 110 onto the coils 26. A cap 114 is suitably aflixed to the tray 110 to deflect the stream of water from the line 30 downward into the tray 110. Overflow weirs 116 are also provided on trays 110 to prevent an excessive accumulation of Water therein.

Referring specifically now to the composition of the 4 coil 26 in the chiller 12, a preferred range of elements for the stainless steel is as follows:

Range, percent by Wt.

Carbon 0.04-0.08 Manganese 0.20-1.00 Silicon 0.40-1.00 Chromium 10.50-11.75 Nickel 0.20-0.50 Titanium 0.20-0.75 Iron Balance Specific compositions which have proven themselves successful in practice are the following:

I II III Percent by weight:

Carbon 0.04 0.08 0.08. Manganese.

1 o. Chromium 75..- 10.5011.75. Nickel 0. Titanium 0.50 5 0.35-0.75.

.75. Iron Balance Balance".-- Balance.

As is manifest to those skilled in the art, the above compositions would nonmally contain therein trace amounts of sulphur and phosphorus, each generally being within the range of 0.025-0.05%, again by weight.

The composition employed in constructing a coil structure for use in the chiller package of this invention has been found to have the following physical properties:

Utilizing non-hardening ferritic stainless steel compositions within the range indicated avoids the necessity in chiller applications of periodically adding inhibitors or other water treatment materials. A typical inhibitor composition includes between 500/1000 parts of sodium chromate and 1- /2 to 3% borax. This mixture is available in powder or granular form, and when used with mild steel galvanized tubing of the prior art, was designed to prevent tube corrosion. However, inhibitors have been found to reduce to a degree the heat transfer coefiicient of the coils, and have not been completely successful in avoiding the formation of scale deposits on the coils and the consequent formation of crevices in the coil presumably attributable to the action of chloride and bicarbonate ions. The coil structure of this invention, on the other hand, when formulated of a material within the range above set forth, has been found after passivation treatment, as in 10% nitric acid and 1% hydrofluoric acid, to present exceptional resistance to attack from various field tap waters at chilled water temperatures in aerated systems.

The chiller construction shown in FIGURE 1 of the drawings incorporates, as was earlier noted, a spaced wall construction having therein foamed insulation. However, it is also within the contemplation of this invention that the chiller wall may be constructed of a single shell, utilizing the stainless steel composition disclosed herein. A construction of this type is illustrated in FIGURE 2, and embodies a coil arrangement 26a of the same type as shown in FIGURE 1, and also includes a shell or casing 120 surrounded by any suitable insulative material 122, such as a glass fiber matte or foamed plastic, held in place by strapping 124 or other suitable means.

A range of elements of the chiller coil construction has been set forth above, and of course, variations can be practiced therein without departing from the novel concepts of this invention. Similarly, those skilled in the art can readily comprehend that it may be desirable to utilize this broad range and variations therein in other portions of the refrigeration system.

' I claim:

1. A refrigeration system which comprises a generator, an absorber, a condenser and an evaporator which has heat exchange surfaces therein, said surfaces being constructed of a nonhardening ferritic stainless steel alloy containing 0.04 to 0.08% carbon, 0.20 to 1.00% manganese, 0.40 to 1.00% silicon, 10.50 to 11.75% chromium, 0.20 to 0.50% nickel, 0.20 to 0.75% titanium, and the balance iron, each being in percentages by weight.

2. A refrigeration system as defined in the stainless steel is composed of: 0.04% manganese, 0.40% silicon, 11.00% chromium, nickel, 0.50% titanium and the balance iron.

3. A refrigeration system of the character defined in claim 1, wherein the stainless steel is composed of: 0.08% carbon, 1.00% manganese, 1.00% silicon, 10.50 to claim 1, wherein carbon, 0.50% 0.20%

6 11.75% chromium, 0.50% nickel, 5 XC or 0.75 titanium and the balance iron.

4. A refrigeration system as defined in claim 1, wherein the stainless steel is composed of: 0.08% carbon, 0.20 to 1.00% manganese, 1.00% silicon, 10.50 to 11.75 chromium, 0.50% nickel, 0.35 to 0.75% titanium and the balance iron.

5. A refrigeration system as defined in claim 1, wherein the heat exchange surfaces take the form of a tubular coil member.

References Cited UNITED STATES PATENTS 2,153,977 4/1939 Wilkins 165-133 2,298,996 10/1942 Woods 165133 2,745,797 5/1956 Long 62-85 LLOYD L. KING, Primary Examiner US. Cl. X.R. 

